Shoe comprising a sole of a thermoplastic material and a method for use in manufacturing such a shoe

ABSTRACT

The present invention pertains to a new shoe comprising a sole of a thermoplastic material adhered to an upper shoe with a hot melt adhesive that is applied between the sole and the upper shoe, wherein the hot melt adhesive is fused with the thermoplastic material. Advantageously, the fusion is brought about by heating the hot melt adhesive to a temperature THM such that it softens, heating the second body such that the thermoplastic material that has a melting temperature TM obtains a temperature TSUB below TM while making sure that (THM+TSUB)/2 is equal to or higher than (TM−10° C.).

GENERAL FIELD OF THE INVENTION

The present invention pertains to shoes and the manufacturing thereof.More particularly the invention pertains to shoes with a sole of athermoplastic material and a method for making a workpiece that can beused in the manufacturing of such shoes.

BACKGROUND OF THE INVENTION

Contemporary shoes comprise the same basic parts. All shoes have a sole,which is the bottom of a shoe, in contact with the ground. Soles can bemade from a variety of materials, although most modern shoes have solesmade from natural rubber, polyurethane, polyvinyl chloride (PVC) orethylene-vinyl acetate copolymer (EVA). Soles can be simple, a singlematerial in a single layer, but most often they are more complex, withmultiple structures or layers and materials. When various layers areused, soles may consist of an insole (also known as a sock liner), amidsole, and an outsole (i.e. the layer in direct contact with theground). The midsole is the layer in between the outsole and the insole,typically there for shock absorption.

Another common part to all shoes is the upper shoe. The upper shoe helpshold the shoe onto the foot. In the simplest cases, such as sandals orflip-flops, this may be nothing more than a few straps for holding thesole in place. Closed shoes, such as boots, trainers and most men'sshoes, will have a more complex upper. This part is often decorated oris made in a certain style to look attractive. The upper may beconnected to the sole by a strip of leather, rubber, or plastic that isstitched between it and the sole, or it may be glued to the sole byusing an adhesive. In the manufacture of athletic shoes, the upper shoeis in most cases glued to the midsole (the latter being an importantitem for such shoes) using a solvent based adhesive, either using anaqueous solvent (such as water based PUD's, polyurethane adhesives) or anon-aqueous solvent (such as polychloroprene or styrene-isoprene-styreneadhesives). Although solvent-based adhesives are relatively expensive,inherently require a long processing time and also, despite the factthat special care may need to be taken to prevent environmental damageand deleterious health effects (caused by many non-aqueous solvents),such adhesives are preferred over hot melt adhesives. Hot melt adhesiveshave the advantage of being (almost) solvent free and allowing veryshort processing times without any foaming tendency during processing,but the adhering properties on the relatively smooth soles arerelatively bad. This is in particular true when adhering an upper shoeto a sole of a thermoplastic material. The latter type of material wouldin principle be preferred over the commonly used EVA (that is typicallyused for mid-soles) because of its easy recyclability when compared toEVA, the finished foam of which has thermoset properties that preventrecycling by simply melting the material and reprocessing it. Still, dueto the difficulty of gluing an upper shoe to a thermoplastic sole, EVAis still the polymer of choice, using solvent based adhesives to adherethe upper shoe.

The problem of low quality adherence of an upper shoe to a thermoplasticsole, especially when using a hot melt adhesive, has been known sincedecades.

GB 1247855 (filed 1967, published 1971) describes the problem of using ahot melt adhesive to bond the upper shoe to a sole of plasticisedpolyvinyl chloride. The solution proposed in this patent is to use apolyester hot melt adhesive that includes a quantity of a nitrogencontaining organic compound having a polar group, such asN-Butyl-Benzenesulphonamide or N-Ethyl-P-tolylsulphonamide. Suchcompounds however are associated with health hazards.N-Butyl-Benzenesulphonamide is neurotoxic and has been found to inducespastic myelopathy in rabbits. N-Ethyl-P-tolylsulphonamide is toxic andhighly irritating.

U.S. Pat. No. 3,168,754 (filed 1961, published 1965) also mentions theproblem of using a hot melt adhesive for adhering an upper shoe to asole, despite the fact that in other fields than sole attaching, hotmelt adhesives have been found very useful towards the end of the1950's. The '754 patent states (column1, lines 28-30) that “attempts tobond outsoles to uppers using the known hot melt adhesive processes gaveinadequate bonds, apparently because of unsatisfactory penetrationand/or wetting of the surfaces to be bonded.” The solution proposedaimed at increasing the penetration and wetting properties of the hotmelt adhesive by using a process of repeated heating and cooling. Thisincreases process time and still may not provide adequate bonding, inparticular when adhering to a thermoplastic sole.

U.S. Pat. No. 3,212,115 (filed 1959, published 1965) confirms that theuse of hot melt adhesives in the manufacturing of shoes leads to severaldisadvantages, not the least of which is failure of the bond attemperatures involved in the treatment or use of the bonded structuresin practice. The solution proposed is a complicated method involvingdepositing a relatively thick body of a molten, crystallisable hot meltadhesive on a surface, supercooling the adhesive to a temperature belowits crystallization temperature but above its second order transitiontemperature, pressing said body of supercooled adhesive between saidsurface and a second surface to distort the body of adhesive, whereinthe distortion should induce crystallisation and effecting orientationof the molecules of the deposited adhesive to increase the tensilestrength and toughness of the adhesive.

GB 2048897 (filed 1979, published 1980) states (page 1, lines 14-16)that it is known that the receptiveness of elastomeric soling materialtowards adhesives and to thermoplastic materials is oftenunsatisfactory. The solution proposed is to use aggressive primerscomprising an organic halogen donor, like mixtures of isocyanuricchloride and a sulphonamide such as, for example, p-toluenesulphonamide, for promoting adhesion. These primers are toxic,irritating and environmentally unfriendly.

U.S. Pat. No. 6,497,786 (filed 1997, published 2002) describes thepotential advantages of using solvent less adhesives, but indicates thatthe need to heat the adhesives to be able and apply them is adisadvantage, in particular since present-day sole materials may deformat high temperatures. The '786 patent proposes to use microwaves tolocally heat the adhesive while keeping the sole at a low temperature.The solution however needs a very complicated device for specificallyheating the adhesive. Next to this, the problem of inadequate adherencewhen using a hot melt adhesive is neither addressed nor solved.

OBJECT OF THE INVENTION

It is an object of the invention to provide a new shoe and method ofassembling a workpiece that can be used in manufacturing such a shoethat mitigates the prior art disadvantages.

SUMMARY OF THE INVENTION

In order to meet the object of the invention a new shoe has beendevised, the shoe comprising a sole composed of a thermoplastic materialadhered to an upper shoe with a hot melt adhesive that is appliedbetween the sole and the upper shoe, wherein the hot melt adhesive isfused with the thermoplastic material.

The inventors surprisingly found that a good adherence using a standardhot melt adhesive can be obtained, even when adhering to a body of athermoplastic material that has a very smooth surface, when the methodprovides for a fusion of the hot melt adhesive with the thermoplasticmaterial. This finding was based on the recognition that although athermoplastic material per se is less receptive for adhering to anothermaterial, in particular a hot melt adhesive, it provides the option ofmelting an upper region of the body (i.e. a region that has a thicknessbeyond molecular scale, at least being at a micrometer level or beyond,i.e. 1 μm or thicker, e.g. 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 60, 70,80, 90, 100 or more μm's), which on its turn may provide the option ofthe molecules in the molten hot melt adhesive and the molten upperregion of the thermoplastic body to fuse, i.e. to mix and form a newmaterial that acts as a bridge between the hot melt adhesive on the onehand and the thermoplastic body on the other hand.

The invention also relates to a method of assembling a workpiece for usein the manufacturing of the shoe, comprising heating the hot meltadhesive to a temperature T_(HM) such that it softens and can beapplied, heating the thermoplastic body such that the thermoplasticmaterial obtains a temperature T_(SUB) below its melting temperature,such that (T_(HM)+T_(SUB))/2 is equal to or higher than the said meltingtemperature of the thermoplastic material minus 10° C. (T_(M)−10° C.).When applying these specific temperatures, the total heat available issufficient to melt the upper region of the thermoplastic body uponcontact with the hot met adhesive, and fusing the two molten substancesis allowed, in particular when applying pressure, e.g. when applying theupper shoe (wherein the molten hot melt adhesive may have been appliedas such to the sole before applying the upper shoe, or may have beenpre-applied to this upper shoe and kept at a sufficient temperaturewhile in contact with this upper shoe alone). Although the melting of athin upper region of the thermoplastic body could be accomplished invarious ways (using e.g. convection of hot air or a liquid, radiation,etc.) it was found that a very simple way is to use the heat capacity ofthe hot melt adhesive and the body themselves to provide the heat formelting the upper region of the thermoplastic body.

In any case, by providing the fusion between the hot melt adhesive andthe thermoplastic body, a very strong mechanical connection may beobtained, without the need for applying special organic molecules,primers or using complicated heating procedures and equipment.

Definitions

A shoe is an outer covering for the human foot typically having a thickor stiff sole with an attached heel and an upper part (also denoted asthe upper shoe) of lighter material, such as a textile or leathersheeting.

A hot melt adhesive is a thermoplastic adhesive with no (less than 1 or2 wt %) solvent. Upon heating the adhesive softens in order to beapplied to a substrate. Preferably the hot melt adhesive undergoes afirst order phase transition when being heated and transformed from asolid into a liquid.

A thermoplastic material is a material (typically a synthetic polymermaterial) that becomes plastic, e.g. shapeable, upon heating and hardensupon cooling to retain desired shape and is able to reversibly undergothis process repeatedly. The melting temperature (T_(M)) of thethermoplastic material is the peak melting temperature as defined inASTM D3418 measured during the second heating step in a DifferentialScanning calorimetry (DSC) experiment conducted at 10° C./min heatingrate. If multiple peaks are present, then the first peak (e.g. lowesttemperature) corresponding to the melting of the hard block of thethermoplastic elastomer should be taken.

A first order phase transition temperature of a material is thetemperature at which the material undergoes a discontinuous change indensity. Examples of first order transitions are melting (solid toliquid conversion) and evaporating (liquid to gas conversion). Aglass-transition is a second order transition since there is nodiscontinuous change in density.

A body is a solid 3-dimensional object having predetermined dimensions.

To be fused means to unite to form a single entity by melting or as ifby melting, in particular which results in the absence of a borderlineand/or distinct boundary between materials in Scanning ElectronicMicroscopy (SEM) pictures at an enlargement of 500 to 1000 times.

A textile material is a material that is consists in essence (for morethan 50%, for example more than 55%, 60%, 65%, 70%, 75%, 80%, 85%, oreven more than 90%) of fibrous material such as polymeric yarns.

A body being composed of a thermoplastic material means that the basicstructure of the body consists of a thermoplastic material, the materialtypically containing over 50% (on a weight basis), preferably over 60%,70%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or evenup to 100% of a thermoplastic polymer.

A workpiece is an assembly of materials that is used in manufacturing anend product.

A smooth surface is a surface not having a regular or irregular patternof protrusions that are tactually perceived as “rough” by man, i.e. nothaving a pattern of protrusions with an average height above 100 μm,preferably not above 90 μm, 80 μm, 70 μm, 60 μm, 50 μm, 40 μm, 30 μm, 20μm, 10 μm, 9 μm, Bpm, 7 μm, 6 μm, 5 μm, 4 μm, 3 μm, 2 μm or even 1 μm,and a surface not having a regular or irregular pattern of indentationsor cavities that are visually perceived as the inverse of suchprotrusions, i.e. not having a pattern of indentations with an averagedepth of more than 100 μm, preferably not more than 90 μm, 80 μm, 70 μm,60 μm, 50 μm, 40 μm, 30 μm, 20 μm, 10 μm, 9 μm, Bpm, 7 μm, 6 μm, 5 μm, 4μm, 3 μm, 2 μm or even 1 μm.

EMBODIMENTS OF THE INVENTION

A thermoplastic material specifically suitable for the sole of the shoeaccording to the present invention is thermoplastic elastomers.Thermoplastic elastomers (TPE), sometimes referred to as thermoplasticrubbers, are a class of copolymers or a physical mix of polymers whichconsist of materials with both thermoplastic and elastomeric properties.Six generic classes of commercial TPEs can be distinguished: styrenicblock copolymers, thermoplastic olefins, elastomeric alloys,thermoplastic polyurethanes, thermoplastic copolyester and thermoplasticpolyamides.

In an embodiment the shoe according to the invention has a sole thatcomprises a foamed composition comprising a thermoplastic copolyesterelastomer in an amount of 70 to 99 wt % based on the total amount of thefoamed composition. In another embodiment, the foamed compositioncomprises a thermoplastic copolyester elastomer in an amount of 70 to 99wt % and a plasticizer in an amount of 1 to 30 wt % based on the totalamount of the foamed composition. Such compositions are disclosed inWO2018134166. Surprisingly, the inventors have found that the presenceof a plasticizer in combination with a thermoplastic copolyesterelastomer results in the possibility to achieve low density foams whichexhibit less cracks, which are ideally suitable as a sole material inshoes. Lower density crack-free foams are very attractive as it is animportant feature in applications where light-weight is favorable, inparticular in athletic shoes. A foamed composition is herein understoodto be known to a person skilled in the art. Preferably a foamedcomposition has a density of between 0.1 and 0.7 g/cm³, typicallybetween 0.2 and 0.3 g/cm³, especially for use in athletic shoes. Athermoplastic copolyester elastomer is herein understood to be acopolymer comprising hard segments built up from polyester repeatingunits, and soft segments chosen from another type of polymer.

In a further embodiment, the thermoplastic copolyester elastomercomprises hard segments built up from polyester repeating units derivedfrom at least one aliphatic diol and at least one aromatic dicarboxylicacid or an ester thereof, and soft segments chosen from the groupconsisting of aliphatic polyether, aliphatic polyester, aliphaticpolycarbonate, dimer fatty acids and dimer fatty diols and combinationsthereof.

Aliphatic diols contain generally 2-10 C-atoms, preferably 2-6 C-atoms.Examples thereof include ethylene glycol, 1,2-propylene glycol,1,3-propylene glycol, butylene glycol, 1,2-hexane diol,1,6-hexamethylene diol, 1,4-butanediol, 1,4-cyclohexane diol,1,4-cyclohexane dimethanol, and mixtures thereof. Preferably,1,4-butanediol is used. Suitable aromatic dicarboxylic acids includeterephthalic acid, isophthalic acid, phthalic acid,2,6-naphthalenedicarboxylic acid and 4,4′-diphenyldicarboxylic acid, andmixtures thereof. Also very suitable is a mixture of4,4′-diphenyldicarboxylic acid and 2,6-naphthalenedicarboxylic acid or amixture of 4,4′-diphenyldicarboxylic acid and terephthalic acid. Themixing ratio between 4,4′-diphenyldicarboxylic acid and2,6-naphthalenedicarboxylic acid or 4,4′-diphenyldicarboxylic acid andterephthalic acid is preferably chosen between 40:60-60:40 on weightbasis in order to optimize the melting temperature of the thermoplasticcopolyester.

The hard segment preferably has as repeating unit chosen from the groupconsisting of ethylene terephthalate (PET), propylene terephthalate(PPT), butylene terephthalate (PBT), polyethylene bibenzoate,polyethylene naphthalate, polybutylene bibenzoate, polybutylenenaphthalate, polypropylene bibenzoate and polypropylene naphthalate andcombinations thereof. Preferably, the hard segment is butyleneterephthalate (PBT), as thermoplastic copolyester elastomers comprisinghard segments of PBT exhibit favourable crystallisation behaviour and ahigh melting point, resulting in thermoplastic copolyester elastomerwith good processing properties and excellent thermal and chemicalresistance.

Soft segments chosen from aliphatic polyesters have repeating unitsderived from an aliphatic diol, and an aliphatic dicarboxylic acid orrepeating units derived from a lactone. Suitable aliphatic diols containgenerally 2-20 C-atoms, preferably 3-15 C-atoms in the chain and analiphatic dicarboxylic acid containing 2-20 C atoms, preferably 4-15 Catoms. Examples thereof include ethylene glycol, propylene glycol,butylene glycol, 1,2-hexane diol, 1,6-hexamethylene diol,1,4-butanediol, cyclohexane diol, cyclohexane dimethanol, and mixturesthereof. Preferably, 1,4-butanediol is used. Suitable aliphaticdicarboxylic acids include sebacic acid, 1,3-cyclohexane dicarboxylicacid, 1,4-cyclohexane dicarboxylic acid, adipic acid, glutaric acid,2-ethylsuberic acid, cyclopentanedicarboxylic acid,decahydro-1,5-naphtylene dicarboxylic acid, 4,4′-bicyclohexyldicarboxylic acid, decahydro-2,6-naphthylene dicarboxylic acid,4,4′-methylenebis (cyclohexyl)carboxylic acid and 2,5-furan dicarboxylicacid. Preferred acids are sebacic acid, adipic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexane dicarboxylic acid. Most preferred isadipic acid. Preferably, the soft segment is polybutylene adipate (PBA)which may be obtained from 1,4 butanediol and adipic acid.

The soft segment may be aliphatic polyethers, which may comprise unitsof polyalkylene oxides, such as polyethylene oxide and polypropyleneoxide and polytetramethylene oxide and combinations thereof, either asindividual segment or combined in one segment. A combination is forexample ethylene oxide-capped polypropylene oxide.

A preferred soft segment is polytetramethylene oxide (PTMO). Also softsegments comprising a block copolymer in which two types of glycols arereacted to form a soft segment such as based on polyethylene oxide (PEO)and polypropylene oxide (PPO) can be used. The latter is also referredto as PEO-PPO-PEO, as the PEO blocks are at the ends of a soft segmentas PEO reacts best with a hard segment. PTMO, PPO and PEO based softsegments allow for foams having a lower density.

The soft segment may be an aliphatic polycarbonate and is made up ofrepeating units from at least one alkylene carbonate. Preferably asalkylene carbonate repeating unit is represented by the formula:

where R₁=alkyl and X=2-20.

Preferably R₁=CH2 and x=6 and the alkylene carbonate is thereforehexamethylene carbonate, as this provides high heat resistance to thearticle and is readily available.

The soft segment may be dimer fatty acids or dimer fatty diols andcombinations thereof. The dimerised fatty acids may contain from 32 upto 44 carbon atoms. Preferably the dimerised fatty acids contain 36carbon atoms. Also suitable are dimer fatty diols which may be derivedfrom the dimer fatty acids as disclosed above. For example a dimerisedfatty diol may be obtained as a derivative of the dimerised fatty acidby hydrogenation of the carboxylic acid groups of the dimerised fattyacid, or of an ester group made thereof. Further derivatives may beobtained by converting the carboxylic acid groups, or the ester groupsmade thereof, into an amide group, a nitril group, an amine group or anisocyanate group.

In a preferred embodiment the foamed composition comprises athermoplastic copolyester elastomer having hard and soft segments,wherein the hard segment is chosen from PBT or PET, preferably PBT, andthe soft segment is chosen from the group consisting of polybutyleneadipate (PBA) polyethylene oxide (PEO), polypropylene oxide (PPO),polytetramethylene oxide (PTMO), PEO-PPO-PEO and combinations thereof,preferably PTMO, as this provided an article exhibiting low densities.In a further preferred embodiment the foamed composition comprises athermoplastic copolyether-ester elastomer composed of PBT and PTMO.

Plasticizers are known substances to a person skilled in the art per se,and for example lower the hardness and/or increases the strain at breakof the composition as compared to the elastomer itself. Plasticizers arepresent in an amount of between 1 to 30 wt % based on the total amountof the foamed composition, preferably between 5 to 25 wt % and even morepreferred between 8 to 20 wt %. Plasticizers include for examplephthalate esters, dibasic acid esters, mellitates and esters thereof,cyclohexanoate esters, citrate esters, phosphate esters, modifiedvegetable oil esters, benzoate esters, and petroleum oils, andcombinations thereof. Preferably, the plasticizer is chosen from thegroup consisting of Triphenyl phosphate (TPP), tert-Butylphenyl diphenylphosphate (Mono-t-but-TPP), di-tert-butylphenyl phenyl phosphate(bis-t-but-TPP), Tris(p-tert-butylphenyl) phosphate (tri-t-but-TPP),Resorcinol bis (Diphenyl Phosphate) (RDP), dichloropropyl phosphate,Bisphenol A bis-(Diphenyl Phosphate) (BDP), tricresyl phosphate (TCP),triethyl phosphate, tributyl phosphate (TBP), tri-2-ethylhexylphosphate, trimethyl phosphate, epoxidized soybean oil (ESO), epoxidizedpalm oil (EPO), epoxidized linseed oil (ELO), argan oil and combinationsthereof.

To the alternative, the shoe according to the invention comprises a soleof a thermoplastic material adhered to an upper shoe with a hot meltadhesive that is applied between the sole and the upper shoe, whereinthe hot melt adhesive is fused with the thermoplastic material andwherein the sole comprises thermoplastic polyurethane (TPU).Beneficially, the sole comprises TPU in an amount of 70 to 100 wt %based on the total amount of the sole composition. Advantageously, thesole may comprise expanded, i.e. foamed TPU, such as disclosed inWO94/20568 or US2010/0222442. Thermoplastic polyurethanes and processesfor their production are well known. TPU is a block copolymer consistingof alternating sequences of hard and soft segments or domains formed bythe reaction of (1) diisocyanates with short-chain diols (so-calledchain extenders) and (2) diisocyanates with long-chain diols. By varyingthe ratio, structure and/or molecular weight of the reaction compounds,a large variety of different TPUs can be produced. Preferably,polyester-based TPUs are used for soles, for example those derived fromadipic acid esters.

In another embodiment the upper shoe comprises a layer of textilematerial that is contiguous with the sole. A textile material appears tobe ideally suitable to be connected to the sole via a hot melt adhesivewithout any special measures being needed, probably due to the irregularsurface that is provided by the constituting yarns. The textile materialmay comprise polymeric yarns, such as yarns made from polyester polymer.This is particularly advantageous when the sole is also made from apolyester material, allowing easy recycling of the assembly of the uppershoe and sole. Insoles, midsoles and outsoles are all considered a solein the context of this invention.

In an embodiment the hot melt adhesive comprises as a main constituent(i.e. in an amount of at least 50% by weight of the adhesivecomposition) a polymer selected from the group consisting of(co)polyurethane(s), (co)polycarbonate(s), (co)polyester(s),(co)polyamide(s), (co)poly(ester-amide(s), mixtures thereof and/orcopolymers thereof. Preferably the hot melt adhesive comprises a(co)polyester as a main constituent. The (co) polyester may be built upfrom an acid selected from terephthalic acid, isophthalic acid, succinicacid, suberic acid, pimelic acid, adipic acid, fumaric acid, maleicacid, itaconic acid, dimer fatty acid, sebacic acid, azelaic acid,sulfoisophthallic acid or its metal salt, 1,3-cyclohexanedicarboxylicacid, 1,4-cyclohexane dicarboxylic acid, furane dicarboxylic acid,trimellitic anhydride and/or dialkyl esters thereof, mixtures thereoftogether with an alcohol selected from: ethylene glycol,1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, neopentyl glycol,diethylene glycol, triethylene glycol, 1,8-octanediol,2,2,4-trimethyl-1,3-pentanediol, polyethylene glycol, polypropyleneglycol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol,2,4-dimethyl-2-ethylhexane-1,3-diol, 2,2-dimethyl-1,3-propanediol,2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol,1,3-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol,1,4-butanediol, dimer fatty acid diol, glycerol, pentaerythrithol,di-pentaerythritol and/or mixtures thereof. Dimer fatty acids, dimerfatty diols and/or dimer fatty diamines (e.g. available from Croda) mayalso be used as potential building blocks to obtain the polymer.

Preferably, the (co)polyester is obtained and/or obtainable fromreacting at least one acid selected from terephthalic acid,2,5-furanedicarboxylic acid, adipic acid, fumaric acid, dimer fattyacid, sebacic acid, azelaic acid, succinic acid, and/or combinationsthereof with at least one alcohol selected from ethylene glycol,1,6-hexandediol, 1,4-butanediol, dimer fatty acid diol and/orcombinations thereof.

The esterification polymerisation processes for making the polyester foruse in the invention composition are well known in the art and need notbe described here in detail. Suffice to say that they are normallycarried out in the melt optionally using catalysts such as titanium- ortin-based catalysts and with the provision for removing any water (oralcohol) formed from the condensation reaction. Preferably if thepolyester resin comprises carboxylic acid functionalities, they arederived from a polyacid and or anhydride.

In yet another embodiment, the upper shoe, the hot melt adhesive and thesole are made from a polyester material.

In again another embodiment of the shoe according to the invention thehot melt adhesive is semi-crystalline (i.e. it at least partlytransforms into crystals when solidifying under equilibrium conditions),preferably having a melting enthalpy between 1 and 80 J/g, morepreferably between 5 and 60 J/g and even more preferably between 10 and40 J/g. The determination of the melting enthalpy is based on ASTMstandard D3418 (“Standard Test Method for Transition Temperatures andEnthalpies of Fusion and Crystallization of Polymers by DifferentialScanning calorimetry”) using a Mettler STARe differential scanningcalorimeter. For the actual measurement an adhesive sample ofapproximately 10 mg is placed in a sample cup. This sample is kept in anoven for 15 minutes at 150° C. After this, the sample is cooled to 50°C. and then heated to 250° C. at a speed of 5° C./min. The sample iskept at 250° C. for 1 minute and thereafter directly cooled to 25° C. ata speed of 5° C./min. From the obtained DSC data the melting enthalpy ofthe sample polymer is obtained.

As indicated here above, the present invention is also embodied in amethod of assembling a workpiece that can be used to manufacture a shoeaccording to the invention, which workpiece comprises a first body (i.c.the upper shoe) mechanically connected to a second body (i.c. the sole)by adhering the first body to a surface of the second body, the secondbody being composed of a thermoplastic material that has a meltingtemperature T_(M), the method comprising:

-   -   Heating a hot melt adhesive to a temperature T_(HM) such that it        softens;    -   Heating the second body such that the thermoplastic material        obtains a temperature T_(SUB) below T_(M);    -   Applying the heated hot melt adhesive to the surface of the        heated second body;    -   Applying the first body to the second body to form the        workpiece;    -   Cooling the workpiece such that the hot melt adhesive hardens;    -   Wherein the temperatures are chosen such that (T_(HM)+T_(SUB))/2        is equal to or higher than (T_(M)-10° C.).

The technical features of any of the above described specificembodiments of the shoe according to the invention can also be combinedwith this method.

In another embodiment of the method of assembling a workpiece the secondbody is heated in its entirety. Such heating can for example beestablished by warming the whole second body in an oven or microwave orin a heated mold. Such heating thus differs from partial heating of theupper region, which can be achieved by external radiation or convection,i.e. heating only the outer side of the second body.

Particularly, in this method the temperatures are chosen such that(T_(HM)+T_(SUB))/2 differs from T_(M) by a number of degrees chosen fromthe group consisting of −10, −9, −8, −7, −6, −5, −4, −3, −2, −1, 0, +1,+2, +3, +4, +5, +6, +7, +8, +9, +10, +11, +12, +13, +14, +15, +16, +17,+18, +19 or +20° C. A higher number leads to a larger part of the upperregion of the thermoplastic body to be melted. However, advantageously,this part should not become too thick, since it will not increase thebonding strength, but may negatively influence the shape and mechanicalproperties of the thermoplastic body. Hence the preferred upper limit of20° C.

In yet a further embodiment, the second body is heated such that thethermoplastic material obtains a temperature T_(SUB) that is at most X °C. less than T_(M), X being chosen from the group that consists of 100,90, 80, 70, 60, 55, 50, 45, 40, 35 and 30. It was found that thethermoplastic body preferably is not heated to temperature too close toits melting temperature.

The invention will now be further explained using the following nonlimiting examples.

EXAMPLES

FIG. 1 schematically shows the interaction between hot melt adhesive andvarious substrates.

FIG. 2 schematically shows the constituting parts of a workpiece for usein the manufacture of a shoe.

FIG. 3 schematically shows a cross section of a material used for anupper shoe of an athletic shoe.

FIG. 4 schematically shows a test set-up for measuring the strength of amechanical connection brought about by a hot melt adhesive.

FIG. 5 is the SEM picture from the connected thermoplastic bodies ofexample 1.

Example 1 describes the connection of two thermoplastic bodies using ahot melt adhesive.

FIG. 1

FIG. 1 schematically shows the interaction between hot melt adhesive 4and various substrates (200, 200′ and 200″). In FIG. 1A, the interactionbetween a layer 4 of hot melt adhesive in its hardened form (thus afterapplication in liquid form and subsequent cooling down to below itssolidification temperature) and a non-smooth surface of a body 200 isdepicted. The surface of the body has various protrusions (201) andindentations (202) which serve as anchoring point for the hardened hotmelt adhesive. This brings about a good mechanical connection betweenthe hot melt adhesive 4 and the body 200.

In FIG. 1B, a situation is depicted wherein the body 200′ has a smoothsurface, leading to the absence of anchoring points for the hot meltadhesive 4. This means that the mechanical connection, if any, betweenthe layer of hot melt adhesive 4 and the body 200′ is very weak. Thelayers can be easily separated by using a slight pulling force to eitherof the layers.

In FIG. 1C the situation is depicted where body 200″ is made of athermoplastic material and the hot melt adhesive is heated sufficientlyjust before application thereof, to make sure that the upper region ofthe body 200″ is heated to above its melting temperature. This way, themolecules of the molten hot melt adhesive and the molten body 200″ maybe able to mix and unite (to fuse) to form one new intermediate material204, which material may ultimately (after solidification of all moltenmaterial) serve as a mechanical bridge between the layer of hot meltadhesive 4 and the body 200″. Although indicated in the schematicrepresentation of FIG. 1C as individually identifiable layers, inpractice the layers 4 and 200″ gradually change from one pure materialto another with the mixed material of a gradually changing compositionin between.

FIG. 2

FIG. 2 schematically shows in a cross section the constituting parts ofa workpiece 1 for use in the manufacture of a shoe (which need not bemore than the workpiece itself). In the figure, part 2 is the (mid-)soleof the shoe, in this case consisting of a foamed composition comprisinga copolyether-ester elastomer (55 wt % PTMO and 45 wt % PBT with respectto the amount of copolyether-ester elastomer) in an amount of 85 wt %,and 15 wt % epoxidised soybean oil as a plasticizer with respect to thetotal amount of foamed composition, leading to a foam having a densityof 0.24 g/cm³ and having T_(M) of 160° C. The upper shoe 3 consists of atextile base layer and a top coat of polyurethane (see FIG. 3). Part 30is a segment of the upper shoe 3 that is used for adhering the uppershoe 3 to the sole 2 using a hot melt adhesive (see Example 1). Indotted lines an outer sole 20 is depicted.

FIG. 3

FIG. 3 schematically shows a cross section of a material used for anupper shoe 3 of an athletic shoe. The upper shoe 3 consists of a textilebase layer 31 and a top coat of polyurethane (32). The textile layer 31is the layer that will be used to make the connection with the sole asindicated in FIG. 2.

FIG. 4

FIG. 4 schematically shows a test set-up for measuring the strength of amechanical connection brought about by a hot melt adhesive (in line withstandardised method ASTM D3936). In this set-up, two bodies 2 and 3having a width L are mechanically connected with a layer of hot meltadhesive 4. These layers are separated at one of the ends, exerting aseparating force F. To make adequate shoes, F/L should be larger than 30Newton per inch (larger than 11.8 Newton per cm).

Example 1

Example 1 describes the connection of a thermoplastic body using a hotmelt adhesive. In order to assess whether a hot melt adhesive could beused to adhere a first body to a thermoplastic body, two thermoplasticbodies were chosen, in this case foamed thermoplastic bodies asdescribed in connection with FIG. 2. The melting temperature T_(M) ofthese bodies is 160° C. (determined with ASTM D3418-03 as described inthis patent application). In a first attempt, a polyester hot meltadhesive having a melting enthalpy of 27±3 J/g was used (thedetermination of which is based on ASTM standard D3418 using a MettlerSTARe differential scanning calorimeter), showing a first ordertransition temperature (solid to liquid) around 110° C. The hot melt washeated to a temperature of 180° C., thus well above its meltingtemperature and at a level that is common for using this hot melt toobtain strong connections. The thermoplastic bodies were preheated tovarious temperatures, ranging from 80° C. to 100° C. before the hot meltadhesive was applied, meaning that (T_(HM)+T_(SUB))/2 varied from 130 to140° C., i.e. 30° to 20° below T_(M). Directly after application of theadhesive, both bodies were pressed together. In none of the cases a goodmechanical connection could be obtained. F/L was less than 5 N/inchvalue for each workpiece. This confirmed the common knowledge thatthermoplastic materials cannot be adequately connected using a hot meltadhesive.

In a second attempt, the hot melt adhesive was heated to 210° C. (i.e.still well below the temperature at which the polyester hot meltadhesive would (start to) degrade, i.e. around 250° C.) and thethermoplastic bodies to a temperature ranging from 120 to 130° C.,meaning that (T_(HM)+T_(SUB))/2 varied from 165 to 170° C., i.e. 5° to10° over T_(M). Either one or both sides of the bodies were providedwith the melted adhesive. In addition to the type of polyester adhesiveused in the first experiment (“Type 1”), another type was used (“Type2”). Keeping all other variables the same as in the first experiment,this way a very good mechanical connection between the two thermoplasticbodies could be obtained. The data are indicated in table 1 below. InFIG. 5 a Scanning Electronic Microscopy (SEM) picture is shown, whichdemonstrates that at an enlargement of 650 times no boundary between thethermoplastic bodies can be distinguished for the example with the Type2 adhesive. In FIG. 5 the upper shoe 3 is connected to midsole 2 in thesame way as is schematically depicted in FIG. 2.

This makes clear that the provision of a connection with a (very) highmechanical strength can be obtained for various hot melt adhesives,without relying on particular organic binding molecules, primers orcomplicated heat-cool cycles, simply by choosing the temperatures suchthat (T_(HM)+T_(SUB))/2 is equal to or higher than (T_(M)−10° C.).

TABLE 1 Strength of mechanical connection using various hot meltadhesives Load at failure Hot melt application Adhesive (N/inch) CommentOne sided Type 1 49.1 — One sided Type 1 47.3 — Two sided Type 1 40.6 —Two sided Type 1 44.0 Two sided Type 1 n.a. Foam rupture* Two sided Type2 98.2 — Two sided Type 2 n.a. Foam rupture* Two sided Type 2 n.a. Foamrupture* *Foam rupture means that the bond was stronger than theintrinsic tear strength of the thermoplastic foam.

Above experiments were also conducted using thermoplastic bodiesconsisting of a foamed composition comprising TPU. Similar results wereobtained and connections with high mechanical strengths were providedaccordingly.

1. A shoe comprising a sole composed of a thermoplastic material adheredto an upper shoe with a hot melt adhesive that is applied between thesole and the upper shoe, wherein the hot melt adhesive is fused with thethermoplastic material.
 2. A shoe according to claim 1, wherein the solecomprises a foamed composition comprising a thermoplastic copolyesterelastomer in an amount of 70 to 99 wt % based on the total amount of thefoamed composition.
 3. A shoe according to claim 2, wherein the foamedcomposition comprises a thermoplastic copolyester elastomer in an amountof 70 to 99 wt % and a plasticizer in an amount of 1 to 30 wt % based onthe total amount of the foamed composition.
 4. A shoe according to claim2, wherein the thermoplastic copolyester elastomer comprises hardsegments built up from polyester repeating units derived from at leastone aliphatic diol and at least one aromatic dicarboxylic acid or anester thereof, and soft segments chosen from the group consisting ofaliphatic polyether, aliphatic polyester, aliphatic polycarbonate, dimerfatty acids and dimer fatty diols and combinations thereof.
 5. A shoeaccording to claim 4, wherein the hard segments are chosen from thegroup consisting of ethylene terephthalate (PET), propyleneterephthalate (PPT), butylene terephthalate (PBT), polyethylenebibenzoate, polyethylene naphtalate (PEN), polybutylene bibenzoate,polybutylene naphtalate, polypropylene bibenzoate and polypropylenenaphtalate and combinations thereof and the soft segments are chosenfrom the group consisting of aliphatic polyether, aliphatic polyester,aliphatic polycarbonate, dimer fatty acids and dimer fatty diols andcombinations thereof.
 6. A shoe according to claim 5, wherein the hardsegment is chosen from PBT or PET and the soft segment is chosen fromthe group consisting of polybutylene adipate (PBA), polyethylene oxide(PEO), polypropylene oxide (PPO), polytetramethylene oxide (PTMO),PEO-PPO-PEO and combinations thereof.
 7. A shoe according to claim 1,wherein the upper shoe comprises a layer of textile material that iscontiguous with the sole.
 8. A shoe according to claim 7, whereintextile material comprises polymeric yarns.
 9. A shoe according to claim8, wherein polymeric yarns comprise polyester polymer.
 10. A shoeaccording to claim 1, wherein the hot melt adhesive comprises a polymerselected from the group consisting of (co)polyurethane(s),(co)polycarbonate(s), (co)polyester(s), (co)polyamide(s),(co)poly(ester-amide(s)), mixtures thereof and/or copolymers thereof.11. A shoe according to claim 10, wherein the hot melt adhesivecomprises a (co)polyester.
 12. A shoe according to claim 1, wherein thehot melt adhesive is semi-crystalline, preferably having a meltingenthalpy between 1 and 80 J/g.
 13. A method of assembling a workpiececomprising a first body mechanically connected to a second body byadhering the first body to a surface of the second body, the second bodybeing composed of a thermoplastic material that has a meltingtemperature T_(M), the method comprising: Heating a hot melt adhesive toa temperature T_(HM) such that it softens; Heating the second body suchthat the thermoplastic material obtains a surface temperature T_(SUB)below T_(M); Applying the heated hot melt adhesive to the surface of theheated second body; Applying the first body to the second body to formthe workpiece; Cooling the workpiece such that the hot melt adhesivehardens; Wherein the temperatures are chosen such that(T_(HM)+T_(SUB))/2 is equal to or higher than (T_(M)−10° C.).
 14. Amethod according to claim 13, wherein temperatures are chosen such that(T_(HM)+T_(SUB))/2 differs from T_(M) by a number of degrees chosen fromthe group consisting of −10, −9, −8, −7, −6, −5, −4, −3, −2, −1, 0, +1,+2, +3, +4, +5, +6, +7, +8, +9, +10, +11, +12, +13, +14, +15, +16, +17,+18, +19 or +20° C.
 15. A method according to claim 13, wherein thesecond body is heated such that the thermoplastic material obtains atemperature T_(SUB) that is at most X ° C. less than T_(M), X beingchosen from the group that consists of 100, 90, 80, 70, 60, 55, 50, 45,40, 35 and
 30. 16. A method according to claim 13, wherein the secondbody is heated in its entirety.
 17. A workpiece obtainable by a methodaccording to claim 13.